Golf balls can be formed from a variety of compositions. Balata, a natural or synthetic trans-polyisoprene rubber, has been used to form golf ball covers. The softness of the balata cover allows the player to achieve spin rates sufficient to more precisely control ball direction and distance, particularly on shorter shots. However, balata covers lack the durability required by the average golfer, and are easily damaged. Accordingly, alternative cover compositions have been developed in an attempt to provide balls with spin rates and a feel approaching those of balata covered balls, while also providing a golf ball with a higher durability and overall distance.
Ionomer resins (e.g., copolymers of olefin, such as ethylene, and ethylenically unsaturated carboxylic acids, such as (meth)acrylic acids, wherein the acid groups are partially or fully neutralized by metal ions) have also been used as golf ball cover materials. Ionomer covers may be virtually cut-proof, but in comparison to balata covers, they display inferior spin and feel properties.
Polyurethanes and polyureas, by providing soft “feel,” have also been recognized as useful materials for golf ball covers. However, conventional polyurethane covers do not match ionomer covers with respect to resilience or rebound. Unsaturated components (such as aromatic diisocyanate, aromatic polyol, and/or aromatic polyamine) used in a polyurethane or polyurea composition may at least in part attribute to the composition's susceptibility to discoloration and degradation upon exposure to thermal and actinic radiation, such as ultraviolet (UV) light. Conventional polyurethane covers can be prone to absorption of moisture, which is another mechanism through which desirable physical properties in the cover may be compromised.
Therefore, a continuing need remains for novel material compositions usable in forming golf ball portions (e.g., covers) having desirable and/or optimal combination of feel, resilience, cut, scratch and abrasion resistance, and interlayer adheresion, and capable of enhencing overall performance characteristics of the golf balls.